Metallic article and its manufacture



Sept. 26, 1939. w. P. FWZ-RANDOLPH 2,173,834

METALLIc. ARTICLE AND I'rs HANUFAc'rURn Filed lom.' v, 19:51 2 sheetssheet 2 INVENTOR. wlLLlAM F. FWzRANDoLF-H satelites sept, es, .tsss

IVIETAILIC ARTICLE TES William P. Fitz-Randolph, Niagara Falls, N.. Y.,

assignor to The Carborundnm Gompany, Nlagara Falls, N. Y., a corporation ci Delaware Application October '-1, 1937, Serial No.. l6l,ii

4 Cla.

ily molded and sintered at a low temperature, l

and which at the same time forms a harder or more'wear resistant article, than ordinarily produced by the sintering of low melting metals and alloys. Another object is-to provide a metallic mixture in which the composition of the finished product, and hence the toughness and other physical properties of the material, can be varied by the time and temperature employed during the sintering process. is to produce an improved metal bonded abrasive article, and particularly one containing diamonds. Another object is to produce a satisfactory metal bond for diamonds which matures at a relatively low temperature, as for example, below a red heat, at which temperature the original hardness and physical properties of the diamond are not impaired. These and `other objects will be apparent from the following description.

In the metal bonding of diamonds, it has been considered necessary to employ high melting metals or alloys to secure satisfactory wear resistance for the meta-l matrix. .y The low melting metals are usually quite soft, and would vnot be expected to provide satisfactory wear resistance for a Wheel intended to cut .extremely hard materials.

,For this reason the commercial metal bonded.

diamond wheels have been restricted to those containing such hard bonds 'as iron, sintered tungsten carbide, and alloys containing molybdenum or 40 other hard ingredients.

essarily be sintered at high temperatures, with consequent danger of impairing the physical properties of the diamonds by the action of heat.

l have found that certain alloys of iron with tin and Zinc can besintered at`temperatures as low as from 300 to 600 C., and that thesealloys `form Very satisfactory abrasive bonds. 1n addition to the low sintering temperature of the alloys, they retain to a considerable extent the proper- 5G` ties of a hard high melting metal. Iron forms very hard intermetallic compounds with tin and,

Zinc, but as these compounds are formed only slowlyat low temperatures, the mixture during incipient sintering consists'merely of iron particles embedded in a tin or zinc matrix. The iron,

A further object These alloys must nec- (ci. si-sso) however, is very hard compared with the tin or zinc, and as the low melting' metal is alloyed to the surface of the iron particles, the iron particles present a wear resistant surface. As heating is continued, reaction to form an intermetallic com- 5 pound or compounds takes place, and a considerable proportion of the low melting metal becomes used up in the formation of the compound. As the compound formation increases, thehardness of the bond also increases. in the tin rich portion ofthe iron-tin series the compound formed by the reaction of Athe iron and tin is FeSnz; in the case of zinc, the definite compounds formed are FeZn'z and FeZng. rlfhese reactions can be either A incipient or carried to practical completion, de

pending upon conditions or sintering. An interstitial surface layer of intermetallic compound between the i-ron. particles and the low melting metal can be produced at relatively low temperatures. The alloys possess the unusual characteristic of becoming less uid with rising temper- 'ature, since -with increasing reaction velocity the liquid low melting metal is used up in forming the solid compound. This partial fluidity of the mix at low temperatures is very desirable in the 25 case of hot pressing, f Upon completion of the4 raction, however, alloys containing less than 81 per cent tin are'completely solid up to temperatures of about 906 C. The exact nature of the invention will be more 3@ clearly understood 'from a consideration of the accompanying drawings.

in the drawings: 1 i Figure 1 is a simplied equilibrium diagram of the `tin-richportion of the tin-iron series, show'- 35 ingA the reactions which take place between iron and Figure 2 is a similar Vdiagram for the zinciron alloys; y Figure 3 shows a plan view of a metal bonded 40 diamond when which can be made by the process herein descrined, and which is adapted to the "grinding or `cutting of tungsten carbide tools;

Figure 6 is a sectionof a cup wheel in which 5.9*

the abrasive surface can be made from-diamonds and analloy bond of the type herein described; Figure 7 is a section of a' lens grinding disc, in which diamonds can be bonded with a tin-iron or zinc-iron alloy; and

Figure 8 shows a method of sintering such a disc under pressure.

Referring to the drawings in detail, Figures 1 and 2 are the usual type of equilibrium diagram, illustrating the phase changes which occuz` with changes in temperature and composition of the alloy. It will be noticed that the temperature of complete melting rises very abruptly with the addition oi only a small proportion of iron. With the addition of only i9 per cent iron to tin, free tin completelyv disappears from the alloy if heating is continued until equilibrium is reached. It will thus be observed that the initial mixture, if rnade from component metal powders, may contain as much as 8l per cent liquid tin when heated to 232 C., but after reaction has taken place, the alloy formed will contain no liquid or .no free tin at all. Thus the alloy can be varied from about 8l per cent uncombined tin to no uncombned tin by simply varying the sintering conditions. There are very few 'instances in metallurgical practice where such a wide variation in physical'characteristics can-be eiected with no change in the percentages of the original components of the alloy. v

Similar relations obtain with the zinc-iron alloys, 'as is shown in Figure 2. The temperature of complete melting rises very abruptly when only a small proportion ci iron is added -to the zinc. The compounds formed are FeZm and. FeZn'z; the latter compound forms quite readily. The phase designated as epsilon on the diagram consists o a solid solution in which FeZn'z forms the base. Bonds for diamonds within. the range oi compositions up, to about 30 per cent iron can be molded-at low temperatures, but they show many of the characteristics of a high melting alloy bond.

The wheei shown in Figures 3 and 4, which is suitable for the facing or tungsten carbide tools, consists of an abrasive layer 2 and a metal backing layer which can be simultaneously sintered into a coherent mass. rThis mass forms an abrasive ring i which can be mounted on a backing 5 Amade of resin or other suitable material.

if the abrasive ring contains only a cheapA abrasive such as silicon carbide or fused alumina, the entire ring can be made into a portion of homogeneous composition without the necessity of producinga composite structure.

abrasive, however, such as diamonds or boron carbide, it is desirable to produce a composite ring in which only a relatively thin surface layer 2 contains the expensive abrasive material. In producing such a composite ring, it -is a 01desirable to add a cheap abrasive to the backing 3 in approximately the proportions of the abrasive matrix, it stiens the metal and makes it very resistant to wear or abrasion. Thus, even in cases when the additional abrasive does no cutting whatever, it greatly reduces the wheel loss,

which-is ordinarily due to umlercutting` or tearing out of the metal matrix surrounding the i@ diamonds. me addition of materials suchv as If the cutting portion of the wheel contains an expensive silicon carbide to the mix makes possible the use of a comparatively small percentage of diamonds of fairly coarse grit to do the cutting, with practically no Wearing or tearing out of the surrounding matrix. The action of the softer abrasive in making the matrix resistant to Wear is of special importance in theuse of cut 01T wheels for cuttingglass, silicon carbide and other hard materials which inv themselves have abrasive characteristics. During the cutting operation a considerable portion ofthe Wheel isburied in the cut, and the detritus formed in the cut, being nely divided, has a lapping eect upon the metal in which the diamonds are embedded. This lapping or wearing away is prevented by' the presence of the abrasive distributed throughout the matrix between the particles of diamonds.

A detailed method of making an abrasive wheel ofthe type shown in Figures 3 and Llfcan be illustrated by a specic example, although it will be understood that other compositions and methods of molding and sintering can be used. A mixture of for example diamonds of from 80 to 140 grit, 10% silicon carbide of from 180 to about 400 grit, and 80% of powdered lmetal is introduced into the mold to form the 'cutting surface 2. The metal, which preferably consists of powdered components forming the desired alloy, is thoroughly mixed, screened, and inbred with the abrasive. The mix containing the diamonds is accurately leveled oi, and a backing mixture of silicon carbide and' ocu, metal powder is added to the mold to form the backing 3. If the material is tobe cold molded, the entire mass is then pressed vinto a ring under a pressure of,

-for example, from 10,000 to Li0,000 lbs/sq. in.

This ring, after removal from the mold, can be sintered in an atmosphere which is non-reactive with respect to diamonds and the metal used as a bond, without the application of further consolidating pressure; It is desirable, however, to apply a slight` pressure to the ring during sintering in order to prevent warping. The sintering in thecase of the tin alloys can be from 250 to 500 C., although higher temperatures can be used if more complete compound formation is desired. With zinc alloys a temperature oi` After the ring has been sintered, it ready for mounting upon a suitable backing so that it can be used as an abrasive Wheel or lap. 'Ihe backing 5 indicated in Figure 4 may be a reversible -thermoplastic resin, or a backing of metal can lol vo Y

be used, andv the sintered ring soldered to the metal, or sintered directly thereto.

A convenient method of sintering wheels of the general type shown in Figures 3 and 4 is illustrated in Figure 5. .In this figure, the wheels E are spaced between ceramic bats E- and a weight 3 is placed upon the top of the uppermost bat to exert sufilcient pressure v to prevent ,warping into the furnace through the pipel and the' excess gas escapes through the pipe Il.

A number of diier'ent atmospheres, c an be used for the sintering operation. the simplestand most convenient being ordinary illuminating gas. Hydrogen, helium and argon are also very satisfactory. If desired, the under vacuum.

Figure 6 shows Aa section ot acup wheel which wheels can be siptered has been found suitable for the surfacing 'of refractories such as silicon carbide or re clay bricks and shapes. The abrasive layer I3 ma'ycu consist of diamonds bonded with an alloy of 'aine a or tin containing iron, or can consist of a mixture of diamonds, silicon carbide or other abra# sive, and the alloy bond. The backing I4 can be of resin, metal or any suitable material.

A section of a wheel which can be used for the grinding of lenses, in which the bond can be a sintered tin-iron or zinc-iron alloy, is shown in Figure 7. Such a wheel can be made by the method and from the mixes described in connection with the production of wheels of the type shown in Figures 3 and 4. The layer I6 containing the diamonds is rst introduced into the i mold and leveled oi, and the mix to form the backing l1 then added. The backing layer may consist either of powdered metal or a mixture of powdered metal and an abrasive or ller' cheaper than diamonds.

Figure 7 shows diagrammatically a method of sintering a lens grinding disc having a grinding.

surface of metal bonded diamonds, in which pressure is applied' during the sintering process. The furnace chamber 20 is heated by the wire wound resistance element 2l, and the mold 22 is placed upon a'support 23 resting upon the bottom of the furnace. Pressure is applied by means of the screw jack 24. The mold plunger consists of a cylinder 25 which is bored to receive the pin'26. This pin also extends through the bottom or curved portion of the mold. In assembling the mold, the pin and the'outer ring i21 are placed in po'sition with 4respect .to the curved portion 22, the powdered mix 2 8 is introduced into the mold around the pin i2 6L The cylindrical plunger 25 is then inserted.so as to fit into the ring and at the same timel surround the upper portion of the central pin. The mold parts are preferably made of hard carbon, but can also be made of heat'resistarit metal if desired. The mix can be compressed during the heating process from loose powder, or the articles can be pre-formed by cold pressing before thel combined application of pressure and heat. This.

latter procedure results in a very dense article.

The alloy compositions which have' been found most satisfactory for molded articles, and especially for diamond abrasive, are those containing up to about 30 per cent iron, as these compositions mold readily andcan be sintered at low temperatures. Higher iron compositions can be used, .butjn the intermediate composition range free tin no longer exists in the alloy if complete reaction takes place. It is desirable .product.

.about 30%.

in such cases'to control the sintering operation so Vas to retain some uncombined tin, and conse- .quently some uncombined iron, in the -final` Although I have described the production of the alloys from their component metals during the sintering of the article, comminuted previously alloyed material can be used if desired. The use of component metals, however, has a number of advantages such as increased plasticity of the'originalmix, and the possibility of altering the physicalproperties of the metal through the degree of compound formation during sintering. With high tin or zinc mixes, the plasticity or fluidity of the mixes may be greater than is desired and previously alloyed material can be mixed with additional tin or zinc to produce a mix having practically any required molding characteristics'.

Ternary alloys containing tin, zinc' and iron up to about 30 per cent iron have been found .to have properties similar to the binary'compositions and can be used in the various articles and with the various methods herein set forth.

The invention can be defined as-being within the scope of the following claims.

1; A metal bonded abrasive article consisting of an abrasive comprising diamonds and a bond therefor composed of asintered mixture of tin and iron powders, the said bond containing not more than about 30% iron.

2. A metal bonded abrasive article consisting of an abrasive comprising diamonds and a bond therefor composed of a sintered mixture of tin and iron powders, the said bond containing uncombined tin and not more than about 30% iron.

3. A metal bonded abrasive article consisting.

therefor composed of a sintered mixture 'of'tin and iron powders, at least a portion of the tin and at least a portion of the iron in said bond being retained in the uncombined state and the iron being present in an amount not more than v WILLIAM P. FITz-RANDOLPP. 55 

